1. Field of the Invention
The present invention relates to a hydraulic system for a vehicle, and more particularly, to a hydraulic system for simultaneously driving an air conditioning compressor and a power steering mechanism.
2. Description of the Related Art
Hydraulic systems used in certain vehicles are designed to simultaneously drive the power steering mechanism and the air conditioning compressor. This arrangement simplifies the design of the vehicle hydraulic system and requires less energy to operate.
A hydraulic system of this type is disclosed in the Japanese Unexamined Patent Publication No. 62-12427. FIG. 8 of this publication shows a hydraulic motor 101 which drives an air conditioning compressor 100, and which is connected to a hydraulic pump 103. A power steering mechanism 102 is also connected to the hydraulic pump 103, in series with the hydraulic motor 101.
The hydraulic pump 103 is driven by an engine and is connected to a first and second fluid bypass conduits or paths 104 and 105. A variable flow rate control valve 106 and a relief valve 107 are disposed in the fluid conduits 104 and 105 respectively. A controller 108 controls the actuation of the flow rate control valve 106 as a function of the driving loads of the air conditioning system.
When the power steering mechanism 102 is not activated, the low fluid pressure in the relief valve 107 causes the valve to block the second fluid conduit 105, and the pressurized fluid to flow through the first fluid conduit 104. When the power steering mechanism 102 is activated and the internal fluid pressure in the relief valve 107 rises, the valve opens, and the pressurized fluid from the hydraulic pump 103 flows directly to the power steering mechanism 102.
The design of the disclosed hydraulic system seems to ignore the significant effect of the normal operation of the steering mechanism. The hydraulic system appears to operate satisfactorily when the steering wheel mechanism 102 is activated while the vehicle is parked or is moving at a low speed, thus allowing the air conditioning system to function within its normal range of operation.
However, when the power steering mechanism 102 and the compressor 100 are operated simultaneously under normal driving conditions, the hydraulic system does not function in a completely satisfactory manner. In fact, the power steering mechanism 102 requires a significantly smaller volume of pressurized fluid as compared to the hydraulic pump 103. If the volume of pressurized fluid which is discharged from the hydraulic pump 103 is adjusted to conform to the normal specifications of the power steering mechanism 102, an insufficient volume of pressurized fluid will be made available to the hydraulic motor 101. To overcome this problem, the capacity of the hydraulic motor could be decreased, in order to raise the rotational velocity of the compressor 100. This design, however, presents another concern, namely reduced power to the compressor 100.
On the other hand, if the volume of fluid from the hydraulic pump 103 were adjusted to conform to the normal specifications of the hydraulic motor 101, an excessive volume of fluid would be discharged to the power steering mechanism 102 when the compressor 100 is not functional, thereby causing a significant loss of energy.